Tracing an ellipse from major axis and given points

[charlycharly]

Hello,

I have a serie of given points but i dont know the minor axis length, could someone know how to trace an ellipse passing through those points?

Ellipse problem.gh (10.0 KB)

[wim (Wim Dekeyser)]

Hi -

@charlycharly

[…] could someone know how to trace an ellipse passing through those points?

That’s not a trivial task to solve.

The following thread has 2 Grasshopper graphs that might get you further:
(The thread contains a link to a longer discussion as well).

Fit points to ellipse

Hi, Is there any .Net or Rhinocommon method that approximates an ellipse from a set of points? Similarly to fit circle from points, but for ellipse? I tried to search in google queries but what I found was based on C++ with additional dependencies. Maybe someone have already had this issue?

Also, we have the “Fit ellipse through points function” feature request on the list as RH-62823.
-wim

[Joseph_Oster]

I can’t help wondering how you know the major axis points but don’t know the ellipse?

Here’s a Galapagos solution:

Ellipse problem_2021Oct29bb.gh (14.1 KB)

P.S. Responded to the wrong person…

[DanielPiker]

If you already have the major axis you could also get the ellipse by intersecting lines with the circle and scale1D:

Ellipse problem.gh (16.1 KB)

For more general ellipse/conic problems I see there’s this recent plugin

The Dominion

[seghierkhaled]

This solution with Python 3.9 and Hops

Ellipse problem.gh (10.2 KB)

from flask import Flask
import ghhops_server as hs
import numpy as np
from skimage.measure import EllipseModel

app = Flask(__name__)
hops = hs.Hops(app)

@hops.component(
    "/ellipse",
    name="Ellipse",
    description="Ellipse from points",
    #icon="",
    inputs=[
        hs.HopsPoint("Points", "P", "List of points",hs.HopsParamAccess.LIST),
    ],
    outputs=[
        hs.HopsString("Result", "R", "Result output"),
    ]
)

def ellipse(points):
    pts = []
    for p in points:
        x = p.X
        y = p.Y
        pt = (x, -y)
        pts.append(pt)

    a_points = np.array(pts)

    ell = EllipseModel()
    ell.estimate(a_points)

    xc, yc, a, b, theta = ell.params

    return [xc,-yc,-theta,a,b]

if __name__ == "__main__":
    app.run()

There are other codes:

Fitting an ellipse to point data

Best-fitting line, circle and ellipse

Fitting an ellipse to a set of data points in python

[akilli (Ethan Gross)]

Is anyone able to install this?

[DanielPiker]

I installed it from PackageManager and it worked

[maje90 (Riccardo Majewski)]

This is one of the cases where OP provided just a single case and then left the thread (i’m joking)
I’d like to try some algorythms but i fear other cases would have a different general situation.

[akilli (Ethan Gross)]

Thank Daniel. Package Manager seemed to work, but then nothing shows up when I restart Rhino. Anyway, it’s not your problem.

[DanielPiker]

I think @daniel.christev is the developer of that one

[seghierkhaled]

Compare results between Python/Hops and Regular components:

Ellipse problem.gh (17.5 KB)

[charlycharly]

Thank you very much for your solution!

[charlycharly]

I had the same problem, you should try with a previous version of hops, it works well with the 0.4.1